The present invention relates to an apparatus for introducing measured or dosed quantities of pulverized or pulverulent materials into a carrier gas stream. This invention is particularly applicable to the operation of injecting solid fuels into a shaft furnace during a metal refining process.
European Patent Application No. 0043606 describes a pneumatic transport device for pulverulent materials, particularly coal and/or lignite dust. A pneumatic current or carrier gas stream is formed by the introduction or entrainment of pulverized particles (i.e., coal dust) into a current of pressurized air, whereby the finely dispersed particles are propelled therethrough. The well know prior art method for effecting this carrier gas stream involves a honeycomb-type rotor having plural chamber means. A typical prior art pneumatic transport device comprises, then, a cylindrical rotor peripherally provided with plural vanes which define individual and corresponding compartments or cells. This rotor will rotate within a housing about its longitudinal axis in a hermetic fashion, so that the pulverized material fed in from the top is conveyed downwardly via the compartments or cells into a current of compressed air, the compressed air serving as a propulsion fluid or carrier gas. This carrier gas thus carries or entrains the pulverized material subsequent to delivery by the compartment or cells.
This well known type of dosing apparatus has certain serious deficiencies and problems. One such problem involves the leakage of very fine particles of the pulverulent material from the cells or chambers into and along both the rotor shaft and rotor bearings. Unfortunately, these extremely fine particles easily migrate into virtually every area of the dosing mechanism including the small circular interstice located between the rotor shaft and the internal surface of the bearing. Although very small, this interstice is necessary in order to avoid undesirable friction.
The incidence of pulverized particle leakage is further aggravated by the difference between the pressure in some areas of the dosing device (atmospheric) and the high pressure of the carrier gas. This leakage presents many serious difficulties. For example, there is an increased risk of premature wear due to seizing caused by the pulverized material. The leakage will also create difficulties in accurately controlling dosage quantities.